1. Field of the Invention
This invention relates to conveyor apparatus for elevating loose bulk material from one level to another and in particular to conveyor apparatus which can be used in relatively confined spaces, as for example, in self-unloading ships, and more particularly to a dual belt conveyor-elevator including a belt take-up apparatus and system including a normal pressure mode for tensioning the outer belt of the dual belt conveyor-elevator under normal operating conditions, and which belt take-up apparatus and system also includes a high pressure mode which develops in the outer belt when the driving power for the dual belt conveyor-elevator is interrupted.
2. Description of the Prior Art
The present invention relates to a dual belt conveyor-elevator such as that illustrated in U.S. Pat. No. 3,805,946 issued to Earl W. Yateman et al. on Apr. 23, 1974, for example.
The aforementioned U.S. Pat. No. 3,805,946 to Yateman et al. comprises a pair of endless belt conveyors, the forward runs of which are juxtaposed in face-to-face edge sealing relation to define a tubular carrier wherein the material being conveyed is clamped between the belts. One belt conveyor (i.e., the "outer" belt conveyor) includes a substantially horizontal, upwardly facing entry portion, an upwardly inclined, downwardly facing terminal portion, and a concavely curved intermediate portion, the entry portion being troughed. The other belt conveyor (i.e., the "inner" belt conveyor) includes a downwardly facing entry portion defining with the entry portion of the first conveyor a bight between the conveyors, an upwardly inclined, troughed, upwardly facing terminal portion, and a convex intermediate portion. Each belt over the upwardly facing portion of its forward run serves as troughed conveyor, and each belt over the downwardly facing portion of its forward run serves as a retainer or hugger belt engaging the troughed carrier portion of the other belt. During normal operation, both belts are maintained in tension by automatic tensioning means.
One problem which may be encountered in the operation of the belt conveyor apparatus of the type shown in the aforementioned U.S. Pat. No. 3,805,946 to Yateman et al., particularly conveyors of this type operating at a higher speed and capacity, is that if the source of driving power of the conveyor is stopped (the outer conveyor belt usually being connected to the source of motive power), while the conveyor is still loaded, the load of material on the substantially horizontal run portion of the outer conveyor belt possesses inertia tending to keep this portion of the outer conveyor belt coasting forward after the source of driving power has been interrupted. While the "coasting" problem is most acute when the lower loading portion of the outer conveyor belt is absolutely horizontal, the coasting problem will still exist for outer conveyor belts having loading portions which are inclined at limited angles upwardly from the horizontal, and the present invention is intended to include any such departures from the horizontal, (defined as being included in the terminology "substantially horizontal"), in which a coasting problem still exists. The upwardly extending portion of the outer conveyor belt beyond the "bight" of the inner and outer conveyor belts also has inertia which tends to cause a coasting of this upwardly inclined portion of the outer conveyor belt, but the coasting tendency of the upwardly inclined portion of the outer conveyor belt is much less than that of the horizontally extending portion of the outer conveyor belt, since the upwardly inclined portion of the outer conveyor belt must help lift the load as it coasts. The net result of this difference in coasting tendencies subsequent to power shutdown of the aforementioned two portions of the outer conveyor belt tends to create slack or reduced tension in the outer conveyor belt at or near the region where the inner and outer conveyor belts come together to define the "bight" portion of the two cooperating belts. The tendency to produce slack in the outer conveyor belt near the bight portion of the two cooperating belts, as just described, may tend to cause spillage in this region of the material being conveyed.
The conveyor unloading system of a ship is generally operated from an independent diesel engine generator which is supplied solely for this purpose and which is independent of other electrical power of the ship.
The dual pressure take-up arrangement for a belt elevator as disclosed in the present application is applicable for use in an "emergency" situation in which the conveyor is stopped by pulling the emergency stop cords, with the conveyor still being fully loaded; and is also applicable for operation during routine stopping, since in many instances the entire conveyor system may have to be shut down because of the overloading of the receiving facilities on shore. While this latter situation would not be designated as an "emergency" stop, nevertheless it means stopping the conveyors fully loaded.